Here are some preview clips of “Summer,” the next episode of Discovery Channel’s Frozen Planet, premiering this Sunday, March 25, at 8pm ET/PT. In the first one, an epic clash between two massive male seals over a female threatens to crush a little seal pup standing near the fray. In the second one, caribou also fight for ladies, with an older caribou showing who’s boss by fending off a series of younger bulls who dare to try and cramp his style with a certain female.